About [[MediaWiki:Page-creation-email-subject/en]]
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This should have explicit GENDER support.
I am a little bit confused by the current message, the page creation email subject reads as: {{SITENAME}} page $1 has been created by {{gender:$2|$2}}. {{gender:$2:$2}} seems to be wrong to me, does user name need gender support? Should it just be: {{SITENAME}} page $1 has been {{GENDER:$2|created}} by $2
In English, it's superfluous in any case, and only used so that it's explicit that GENDER is supported. It doesn't really matter where the GENDER parser function is used. You changed it recently, and functionally, it's still the same...
I see I was referring to https://gerrit.wikimedia.org/r/#/c/45173/1/languages/messages/MessagesEn.php . Hope I didn't confuse you more...